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From:   Jiunn Chang <c0d1n61at3@gmail.com>
To:     skhan@linuxfoundation.org
Cc:     linux-kernel-mentees@lists.linuxfoundation.org,
        paulmck@linux.ibm.com, josh@joshtriplett.org, rostedt@goodmis.org,
        mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
        joel@joelfernandes.org, corbet@lwn.net, rcu@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [Linux-kernel-mentees][PATCH] doc: RCU callback locks need only _bh, not necessarily _irq
Date:   Thu, 27 Jun 2019 16:01:47 -0500
Message-Id: <20190627210147.19510-1-c0d1n61at3@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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The UP.rst file calls for locks acquired within RCU callback functions
to use _irq variants (spin_lock_irqsave() or similar), which does work,
but can be overkill.  This commit therefore instead calls for _bh variants
(spin_lock_bh() or similar), while noting that _irq does work.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Jiunn Chang <c0d1n61at3@gmail.com>
---
 Documentation/RCU/UP.rst | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/Documentation/RCU/UP.rst b/Documentation/RCU/UP.rst
index 67715a47ae89..e26dda27430c 100644
--- a/Documentation/RCU/UP.rst
+++ b/Documentation/RCU/UP.rst
@@ -113,12 +113,13 @@ Answer to Quick Quiz #1:
 Answer to Quick Quiz #2:
 	What locking restriction must RCU callbacks respect?
 
-	Any lock that is acquired within an RCU callback must be
-	acquired elsewhere using an _irq variant of the spinlock
-	primitive.  For example, if "mylock" is acquired by an
-	RCU callback, then a process-context acquisition of this
-	lock must use something like spin_lock_irqsave() to
-	acquire the lock.
+	Any lock that is acquired within an RCU callback must be acquired
+	elsewhere using an _bh variant of the spinlock primitive.
+	For example, if "mylock" is acquired by an RCU callback, then
+	a process-context acquisition of this lock must use something
+	like spin_lock_bh() to acquire the lock.  Please note that
+	it is also OK to use _irq variants of spinlocks, for example,
+	spin_lock_irqsave().
 
 	If the process-context code were to simply use spin_lock(),
 	then, since RCU callbacks can be invoked from softirq context,
-- 
2.22.0